Cataract is a disease in which an eyeball lens becomes opaque to result in a lowered eyesight. It is developed in humans and other animals as well. For example, an oral administration of naphthalene to a house rabbit, which makes a dependable model for human in examining pharmacological action of an anticataract agent, results in vacuolation in and trochoidal change (speichen) of a lens, which are prodomes of cataract, and the amounts of reduced glutathione and cysteine in the lens are found to decrease at this point.
Therefrom an expectation follows that the inhibition of such initial changes in the lens and the inhibition of a decrease in the amounts of reduced glutathione and cysteine in the lens at the aforementioned stage will result in effective prevention of the onset and progress of cataract.